1. Field of the Invention
The present invention relates to a method for evaluating the force for demoulding a tire from a given mold, and more particularly a method for predicting the demoldability of new tread patterns combined with new materials.
2. Related Art
New ranges of tires have to comply with a functional specification based on performance requirements such as adherence, rolling resistance, noise, etc. However, these new ranges also have to have a lowest impact as possible on the cost of manufacturing the tires.
The manufacturing cost comprises the raw materials used, the labor costs for producing the green casings which will make up the tire and also the labor costs for the curing station (time necessary for the vulcanization of the green casing and time necessary for opening the curing mold), and the longer the time necessary for opening the press in which the mold is placed, the less time remains for curing the green casings. In extreme cases, it is impossible to demold the casing after curing.
New tire tread patterns are increasingly complex, thereby increasing the demolding time. Being able to anticipate the demoldability of these new tread patterns avoids a situation in which solutions that are too time-consuming post-curing and are thus too expensive are put on the market. Therefore, there is a need for a predictive tool which would avoid the production of curing molds, the use of which in a plant would not be acceptable from an industrial point of view.
It is possible to produce a curing mold having the new tread pattern and to measure the forces necessary for counteracting the adhesion generated between this curing mold and the green casing during the curing phase. In order to be able to assess the demoldability of new tread patterns, it is possible to produce mold portions with the various tread patterns to be evaluated and to measure, by virtue of a dynamometric axle mounted on each different portion, the forces necessary to overcome the adhesion generated during curing for each solution. However, the major drawback of this solution is that it is necessary to produce the equivalent of a complete mold, this representing a fairly high cost for an exploratory method.
Use can be made of the know-how of operational staff, but this has the consequence that subjective limitations (based on feeling and not on experiments) risk greatly penalizing the definition of new tread patterns and thus having a negative effect on the desired performance requirements.
Patent JP 2012 006 287 discloses a method and a means for assessing, from a portion of tread pattern elements, the forces necessary for the demoldability of tread pattern elements that are more consistent while limiting the cost. That patent describes a method using a “test specimen” that is representative of a part of the tread pattern chosen in the most restrictive region of the complete mold, and the forces necessary for overcoming the adhesion generated on the test specimen are measured in order then to transpose it to larger parts.
However, the adhesion of the green casing to the mold which arises during the curing phase is dependent on a large number of parameters which are difficult to assess as a whole. If the geometric aspect of the tread pattern: dimensions and intrusive geometry, is partially taken into account in this prior art, the impact of the materials used (green casing and mold) is not taken into account. Thus, the physicochemical interactions that arise during the curing phase, the nature of the materials used, their rigidity and the rubbing of the casing against the mold during demolding are not measured.
The composition of the materials of tires is changing rapidly and the nature of the constituents can have a non-negligible effect on the demolding forces. Thus, with one and the same tread pattern, the simple fact of changing the materials of the tires can have a significant impact on demoldability.